1. Field of the Invention
The present invention relates to a system for data transfer. More particularly, the present invention relates to a system for data transfer between microcomputer devices.
2. Description of the Prior Art
Systems for data transfer in which accessing units are decoupled via a multiport RAM memory device are known in the art. In this case, the multiport RAM memory device is used as a coupling device for data between the accessing units.
A multiport RAM memory device having two ports is described in “IDT High-Speed 3.3 V 1Kx8 Dual-Port Static RAM, September 1999”. All data, addresses, and control signals are connected in parallel to a memory device. A high number of signals resulting therefrom is disadvantageous if the accessing units are electrically isolated from one another or if even more accessing units are to be added. Control of the memory device requires a certain outlay, since accessing conflicts must be dealt with by the memory device and by the accessing units.
A protocol controller for data transfer between a first microcomputer device containing a first microprocessor bus, referred to here as a local bus, and a standardized data bus, referred to here as a PCI bus, is described in “PCI 9050, PLX Technology, Inc. 1996”. In this case, the PCI bus is used as a signal connection between two microcomputer devices which are transferring data to one another. Functional separations may only be achieved if all signals to the PCI bus are switched off, i.e., a high resistance state (tri-state) is switched to. Electrical isolation between the two microcomputer devices of this type is impossible, or is only possible at a very high cost, since the number of parallel signals is very high. As a supplement to this, a microcomputer device, referred to here as an interbus interface module for PCI, which is suitable for data transfer via the standardized PCI bus, is described in “IBS PCI DDK UM, Phoenix Contact, 7/2001”
A further multiport memory device is taught by German Patent 199 61 138 C2. In this case, access by multiple accessing units to a single-port RAM is made possible using a time-multiplex system. To provide control signals and address signals, serial-parallel converters are used, and time slot assignment units are used to assign and schedule time control. In this case, the time slot assignment units are implemented as control units which require a very high outlay for implementation and/or programming. Separate implementation and/or programming is necessary for each number of accessing units. The serial-parallel converters convert serially arriving signals in such a way that they are applied in parallel to corresponding ports of a multipart RAM. In order to be able to operate multiple ports, all data signals, control signals, and address signals are necessary for each port, due to which a very high number of signals result at the multiport RAM.
A system for data transfer which decouples a serial connection between two microcomputer devices in such a way that the data to be transmitted or received is buffered, therefore making the microcomputer devices independent of the cycle of the data to be transmitted or received, is taught by German Patent Application 100 26 4 16 A1.
Functions of known components for data transfer via ethernet are described in “Ethernet in der Automatisierungstecnik [Ethernet in Automation Engineering], 2000 by Phoenix Contact GmbH & Co”. Basic functions of hubs and switches are described. These components allow division of systems for data transfer into segments. Multiple microcomputer devices which transfer data to one another may be located within the segments. Mechanisms according to known ethernet standard for addressing the microcomputer devices are schematically described.